Lubricants, especially solid film prelubes, are utilized in several metalworking operations. These metalworking operations can include stamping, drawing, forming, bending, rolling, cutting, grinding, punching, sawing, hobbing, reaming, spinning, extruding, trepanning, coining, swagging and the like. The present invention concerns the use of solid film (dry film) prelubes in the form of aqueous dispersions for such type of metalworking operations, utilized on all types of ferrous and non-ferrous metals used in the automotive, appliance and general manufacturing industries. In these three industries, the term, press working operation, is used to define all mechanical processes where any type of sheet metal is formed into specific shapes by the use of mechanical presses. Such operations can further be categorized as stamping and drawing. The term, stamping, is further used to describe all forming operations where parts are formed from sheet metal such that there is no change in the gauge or thickness of the sheet metal. The term, drawing, is further arbitrarily divided into shallow drawing and deep drawing. Drawing defines all forming operations where there is a change or reduction in the gauge or thickness of the sheet metal. Shallow drawing can be defined as to the forming of a cup or shape no deeper than one-half its diameter with only small reductions in metal gauge or thickness. Deep drawing can be defined as to the forming of a cup or shape deeper than half its diameter with substantial reductions in metal thickness or gauge. Formed parts for the automotive, appliance and general manufacturing industries may be produced by one or a combination of these three fundamental fabrication metalworking operations.
Forming lubricants, especially solid film prelubes facilitate these operations by reducing the friction that occurs between the sheet metal being fabricated and the tooling employed for the forming operation. By reducing the coefficient of friction for the specific forming process, power requirements, tool wear and heat generated during forming operation are all diminished. Heat significantly can affect forming operations by changing the metallurgical properties of sheet metal and tooling. It physically degrades these elements, causes their staining or oxidation and also creates physical and chemical changes in the lubricant affecting its performance. In addition, blocking or adhesion between the sheet metal and tooling is reduced or eliminated during the forming operation, transit and storage of formed parts.
In operations involving automotive, appliance and general manufacturing applications the prevention of blocking or adhesion between the sheet metal and tooling is of extreme importance. In addition, the use of specific metalworking forming lubricants such as solid film prelube aqueous dispersions significantly can reduce or eliminate the production of scrap parts (formed parts rejected due to physical damage) which may result from the failure of some forming lubricants. One major purpose of the presented invention is to provide improved lubrication and corrosion protection to all ferrous and non-ferrous metal forming operations. Forming lubricants, especially solid film prelubes, must be capable of functioning on a variety of sheet metal substrates including cold rolled steel, hot dip galvanized, electrogalvanized, hot rolled steel, galvaneal, galvalume and various aluminum alloys.
All basic steels are formed by the basic oxygen process. After the initial chemical process forming the molten steel, the molten steel is either poured to form ingots or continuously cast slabs. Ingots are then converted to slabs in a primary mill (known as a slabber or bloomer). Slabs are then processed via hot rolling:
a. slab is reheated to approximately 2500.degree. F. in a reheat furnace, PA1 b. reduced to any intermediate gauge or thickness via a series of roughing mills at temperatures around 1800-2000.degree. F., PA1 c. then rolled to a final hot band gauge via a series of finishing mills. Finally the steel is coiled. All cold rolled, galvanized and hot rolled steel sold as pickled and oiled go on to pickling and further processing stages. Finishing mills typically operate at temperatures between 1500-1900.degree. F. PA1 a. Commercial quality (good flatness used in shallow draws): yield strength of 38,000 psi, tensile strength of 52,000 psi, 30 percent elongation for two inches and RB hardness of 55. PA1 b. Drawing quality (deep drawn parts): yield strength of 35,000 psi, tensile strength of 50,000 psi, 36 percent elongation for two inches and RB hardness of 50. PA1 c. Quality Special Killed age-hardened): same properties as those of drawing quality except elongation is 40%. PA1 a. aqueous dispersion is warmed and applied to a warm metal substrate, PA1 b. aqueous dispersion is applied at ambient temperature to a metal substrate at ambient temperature. Depending upon the choice of application, a series of warm ovens may be necessary to evaporate the aqueous carrier, reflow the coating following drying or both. Under normal application conditions, the water readily evaporates leaving a dry, solid film prelube coating on the metal substrate.
Hot rolled steel, also known as hot rolled strip or plate steel, undergoes no further processing. These types of steel are mainly used in applications requiring structural strength and are in thicknesses of 0.060 inch and greater. A large quantity of hot rolled steel is used in deep drawing to produce compressor housings for refrigeration systems used in appliance systems. General manufacturing parts produced include gas cylinders used to store and transport liquefied petroleum gases and acetylene. Such automotive parts formed include vehicle road wheels, axle cases and a variety of chassis sidemembers. The typical mechanical properties of the three quality grades of hot rolled steel are summarized below:
Some hot rolled steel will be used as simply hot rolled sheet and strip while a portion sold as hot rolled pickled and oiled exposes the hot rolled strip to an acid pickling medium (150.degree. F.-180.degree. F.) to remove scale, rinsed with water, then air dried and oiled. A vast majority of hot rolled steel will be used to produce cold rolled steel. The hot rolled steel will be rolled into coils and sent to cold reducing mill for further processing. At the cold mill, rolling oil emulsions are used in continuous cold reducing process to produce a variety of cold rolled steels. Cold rolled steel is used as the base template for future production of a variety of galvanized steels. Galvanized steels are becoming more prevalent in all industries because of the superior corrosion protection offered by zinc coatings applied to cold rolled steel templates. Hot dip galvanized steel is produced by passing cold rolled steel through coating applications of molten zinc. In electrogalvanizing processes, molten zinc is applied to cold rolled steel substrates by a variety of electrostatic coating applications. Other forms of galvanized steels involve zinc alloy coatings such as zinc-iron in galvaneal and zinc-aluminum in galvalume metals.
A wide variety of aluminum alloys are also used in a variety of manufacturing applications.
In several metalworking processes, sheet metal coils are cut into pieces known as blanks which are then stamped or drawn to produce the desired finished parts such as those described earlier. Forming lubricants, including solid film prelubes, are often required to provide corrosion protection against a wide range of varying environmental conditions that sheet metal coils can encounter during storage and transportation. Furthermore, when the sheet metal coil is cut into blanks, the forming lubricant must also be required to provide corrosion protection while blanks are transported to other processing facilities or while awaiting further fabrication between operations.
In the recent past, metalworking forming processes were often tedious and complicated, involving a variety of different product types. Often, sheet metals coils would arrive at a processing site, such as a stamping plant, coated with a rust preventative oil. Between the steps of blanking and the actual forming operation, the rust preventative oil would be removed by a cleaning operation (alkaline cleaner, solvent cleaner or blank wash oil . Some type of forming lubricant would then be applied to the sheet metal immediately prior to the stamping or drawing operation. Such lubricants were typically blends of petroleum hydrocarbon oils and various chemical additions. In the last decade, this tedious process of using separate rust preventative oils and drawing lubricants has been replaced in many operations by the use of a single composition known as a prelube. Whether hydrocarbon oil based or solid film, prelubes are applied at the steel mill during either temper rolling or inspection, as rust preventative oils are prior to shipping. Thus no modifications are necessary within the steel mill to physical equipment or processes to use prelubes. Such prelube compositions are thus not intentionally removed from the sheet metal until after the blanking and forming operations. Thus, the use of such prelube compositions eliminates the cumbersome process of applying and removing the combination of rust preventative oils and forming lubricants before further working with only one composition (whether oil-based or solid film). Prelubes thus must function as both a corrosion preventative and forming lubricant.
Attempts have been made to utilize the superior corrosion protection of the water soluble polyacrylic acid resins in the formulation of single component solid prelube aqueous dispersion compositions. While providing good corrosion protection to the sheet metals treated therewith the acrylic acid polymers are poor lubricants. The prior art has formulated lubricants with the acrylic acid resins in an attempt to provide both lubrication and corrosion protection. Under conditions of actual field use these products were sorely lacking in their ability to provide good lubrication during the hot working of the metal piece upon which they had been coated. If the corrosion protection afforded by water soluble polyacrylic acid resins could be incorporated into a product having superior high temperature lubricating properties an improved and desirable product would be afforded to the art.
One of the most important properties of a prelube composition besides lubrication and corrosion protection is cleanability or removability. The performance benefits offered by solid film prelube compositions, would be nullified if drastic measures were necessary to clean them from the surfaces to which they have been applied. In order to prevent interference with all future processing operations after forming, it is necessary for all traces of the prelube composition to be totally removed from the metal surface of the formed part. In the automotive, appliance and general manufacturing industries, powdered or aqueous alkaline cleaners are the normal chemical compositions utilized for removing prelube and other lubricant compositions. These alkaline cleaners are composed of various mixtures of nonionic biodegradable surfactants, amines and different types of inorganic alkalis. Such compositions are water soluble at the recommended dilutions (concentrations of one to four ounces per gallon) and are strongly alkaline in nature (pH of 10.0-12.0). They are designed to effectively remove all traces of processing lubricants and fluids from the wide variety of metal substrates described earlier including ferrous and non-ferrous metals. Formed parts are cleaned in a variety of system types utilizing spray (15-35 psi), immersion and combinations of both types. Formed parts are exposed to cleaner solutions for varying time increments, ranging from 30 seconds to 3.0 minutes for spray systems and 1.0 to 5.0 minutes for immersion systems. Such cleaner compositions effectively operate over a wide temperature range. Appliance industry parts are cleaned over a wide temperature range from 120.degree. F. to 180.degree. F. In the automotive industry, most formed parts are being cleaned at temperatures from 105.degree. F. to 135.degree. F. Parts formed in general manufacturing industries are cleaned at temperatures over a wide range from 120.degree. F. to 190.degree. F. Many prelube compositions, especially hydrocarbon oil based systems, contain chemical additives that cannot be easily removed with such alkaline cleaners, thereby having serious and detrimental effects on all future processing operations and narrowly limiting the use of such compositions.
An important advantage of the present invention is the improved cleanability (removability) of the solid film prelube composition from all metal substrates versus the other prelubes used on such substrate including hydrocarbon oil based and dry film lubricant compositions. This cleanability advantage also extends to all of the types of sheet metal substrates described earlier.
Sheet metal coils, including those composed of ferrous and non-ferrous metals, coated with prelube compositions can be stored for indefinite periods of time before being stamped or drawn into parts. Many chemical constituents of such prelube compositions can oxidize to varying degrees during these storage periods. Oxidations byproducts from hydrocarbon oil components can adversely affect metal surfaces causing staining, discoloration and etching or pitting of the outer molecular layers of the steel strip. Automotive, appliance and general manufacturing industries require prelube compositions that will protect all metal substrates against conditions of oxidation and will not cause contact staining during storage periods.
Prelubes must be compatible with other processing chemicals and operations following forming operations. Many parts formed in the automotive, appliance and general manufacturing industries often have severe bends or angles formed during fabrication operations. These bends and angles can create flanges, seams or other tight radii where prelube compositions can become entrapped. Even with normal exposure to alkaline cleaners, trace amounts of prelube can remain within these intricate areas out of reach. Thus, although the prelube compositions may be effectively removed from exposed part surfaces, trace amounts of prelube can be volatilized, released and contaminate subsequent processing operations. This potential situation necessitates that such prelube compositions, especially solid film prelube compositions, be compatible with cathodic electrocoat paint primers and adhesives use to bond structural components together as well as any type of post welding operations. Trace levels of contamination cannot interfere with the electrocoat process of deposition of paint primers where resulting craters could lead to potential paint finish problems and corrosion. Likewise, contamination cannot affect the wetting or bonding strength of the structural adhesives. Many formed parts are often welded into sub component parts before final assembly and cleaning so the welding process or welds themselves cannot be affected in any manner. Thus prelube compositions should be compatible with such processing compositions and operations.
A vast majority of prelubes used commercially in automotive, appliance and general manufacturing industries are liquid compositions composed of petroleum hydrocarbon oils and additives. Because of their fluid nature, such compositions tend to become unevenly distributed within coated steel coils on the metal surfaces, collecting or pooling due to capillary action or gravity. The occurrence of this condition can have a drastic effect on prelube performance as film uniformity on the sheet metal strip is critical for superior corrosion protection and successful forming. Thus all of the industries discussed earlier demand a prelube that provides the desirable film uniformity thereby insuring adequate corrosion protection and lubrication required by forming operations, especially severe drawing operations. It is an important performance benefit of the present invention to provide the proper film coverage; eg., uniformity, homogenous and consistent film morphology and structure on all ferrous and non-ferrous sheet metal substrates.
Often, prelube compositions are applied at coverage rates up to 1000-2000 mg/ft.sup.2 in some industries to provide the required performance. The automotive, appliance and general manufacturing industries desire prelube compositions that can offer effective performance at lower coating weights thereby improving overall cost efficiency of the forming operation. It is a desired advantage of the present invention to provide effective performance on all ferrous and non-ferrous substrates at lower coating weights between 50 and 500 mg/ft.sup.2, which substantially improves forming lubricant cost performance.
All prelube compositions must lend themselves to improving housekeeping and cleanliness conditions at the mill and at the manufacturing plant. Often, hydrocarbon oil based lubricants and some dry film prelubes can leak onto machine and work surfaces or volatilize into the atmosphere creating hazardous work environments. Compositions can often create irritation or dermatitis among employees exposed to the compositions on a daily basis. Sometimes, compositions can contaminate floor trenches around forming presses, thereby often reaching waste treatment streams. It is a prime object of the present invention for ferrous and non-ferrous metals to be nonhazardous, worker friendly and safe to use on a continual basis.
Finally, a prelube composition must be compatible with the current waste treatment processes and chemicals. Prelube compositions entering those streams must have minimal to no effect on those streams as well as being chemically capable of being waste treatable. It is another purpose of the present invention to provide prelubes which are compatible with existing waste treatment schemes by both having lower quantities (because of lower coating weights) entering the stream and being treatable by current waste treating processes.
It is another object of the present invention to provide metalworking lubricants, and more specifically, a solid film prelube in the form of an acrylate polymer-fatty triglyceride aqueous dispersion for all forms of ferrous and non-ferrous metals that provides all of the foregoing desirable characteristics, and advantages especially superior corrosion protection and lubrication as well as compatibility with all processing and forming operations.
It is a further object of the present invention to provide a method of coating and lubricating a variety of ferrous and non-ferrous metal substrates that provides all of the foregoing desired advantages. These and other objects of the invention are described below.
A specific object of the invention is to provide a prelube having both superior corrosion and lubrication properties which incorporates as the primary corrosion inhibitor water soluble acrylic acid resins and fatty triglyceride as the primary lubricant.